Charge exchange recombination spectroscopy measurements of ion temperature and plasma rotation in PBX

The primary diagnostic on PBX for ion temperature measurements is charge exchange recombination spectroscopy of low Z ions, wherein fast neutrals from the heating neutral beams excite spectral lines from highly excited states (n>4) of hydrogenic O, C, and He via charge exchange collisions with the respective fully stripped ions. Since the neutral beams on PBX provide relatively low-velocity neutrals (i.e., D° beams at 44 keV), best signals are obtained using the near-UV lines of O7+ (e.g., n=8–7, 2976 Å). Off-line analysis of the Doppler broadened and shifted line profiles includes nonlinear least-squares fitting to a model line profile, while a simplified on-line fast analysis code permits between-shot data analysis.